Chitin is a highly insoluble N-acetylated polymer of xcex2-(1,4)-D-glucosamine. Chitosan is an acid-soluble deacetylated form of chitin. Chitin, chitosan, and derivatives thereof are used in a number of industrial applications, including the production of viscosity control agents, adhesives, chromatography carriers, paper-strengthening agents, flocculent agents, food additives, drugs, and cosmetics.
Chitin can be manufactured by the deproteination and decalcification of crab or shrimp shells. Chitosan can then be obtained by deacetylating chitin with a hot alkali solution. This chitosan production process has a number of unfavorable characteristics. For example, the process requires expensive heat energy and caustic alkali, which is a potential health hazard. The process also produces large amounts of waste, thereby necessitating significant disposal costs. In addition, the supply of shrimp or crab shells is highly dependent upon seasonal and environmental factors, leading to unpredictable limitations on production capacity.
The invention is based on the discovery that unexpectedly high yields of chitosan and chitin can be produced from the fungus Actinomucor taiwanensis and from the fungus Rhizopus azygosporus. 
Accordingly, the invention features a method of producing chitosan or chitin by (1) culturing a Rhizopus azygosporus fungus or an Actinomucor taiwanensis fungus in a medium to form a culture, and (2) isolating chitosan or chitin from the cells. For example, chitosan and chitin can be isolated from the culture by separating the fungal cells from the culture and isolating the chitosan or chitin from the separated cells.
The invention also includes a method of producing chitosan or chitin by (1) culturing a fungus of the family Mucoraceae in a medium useful in the methods of the invention to form a culture, and (2) isolating chitosan or chitin from the fungal culture.
A medium useful for the methods of the invention can include about 5 to 60 g/L (e.g., about 30 g/L) corn steep liquor, about 10-100 g/L (e.g., about 50 g/L) glucose, about 0.01 to 30 g/L (e.g., about 2.5 g/L) ammonium sulfate, or other suitable ingredients.
The methods of the invention allow surprisingly high-yield production of chitosan or chitin from a culture containing a Rhizopus azygosporus or Actinomucor taiwanensis fungus. Further, it has been discovered that a medium containing corn steep liquor, glucose, yeast extract, and ammonium sulfate is capable of increasing the output of chitin and chitosan from a fungal culture. The methods of the invention, therefore, provide an alternative to producing chitin and chitosan without reliance on environmentally harmful chemicals or the variable abundance of the crustacean crop.
Other features or advantages of the present invention will be apparent from the following detailed description, and also from the claims.
The invention relates to high yield production of chitosan or chitin from fungal cultures belonging to the family Mucoraceae.
Particular fungi useful in the methods of the invention include Rhizopus azygosporus and Actinomucor taiwanensis. Both of these organisms are available upon request from the Culture Collection and Research Center (CCRC), Food Industry and Research Development Institute, No. 331, Shih-Ping Road, Hsinchu 300, Taiwan, Republic of China. R. azygosporus is available as Catalog No. CCRC31558, and A. taiwanensis is available as Catalog No. CCRC31559.
Procedures for culturing fungi are well known in the art. For example, YM agar can be inoculated with a fungus, and the inoculated agar incubated at 25xc2x0 C. to 37xc2x0 C. for 3 to 6 days. Spores obtained from the fungus are suspended in liquid to achieve a 104 to 107 cfu/ml stock. This stock is directly inoculated into a fermentation medium.
The fermentation medium can have an initial pH ranging from 3 to 8 and can contain 10 to 100 g/L of a carbon source (e.g., glucose, sucrose, corn starch, molasses, or soybean oil), 5 to 60 g/L of a nitrogen source (e.g., soybean meal, peptone, or corn steep liquor), 0.5 to 20 g/L of yeast extract, 0.01 to 30 g/L (NH4)2SO4, 0 to 3 g/L K2HPO4, 0 to 3 g/L NaCl, 0 to 15 g/L MgSO4.7H2O, and/or 0 to 0.3 g/L CaCl2. The fungus is grown in the fermentation medium for an additional two to four days.
Chitosan can be isolated and purified from fungal mycelia by standard methods. For example, alkaline and acid treatment can be used to isolate chitosan as described in McGahren et al., Process Biochem 19:88-90, 1984. Additional details and procedures for isolating chitosan can be found in European Application No. 0531991 A2; Yokoi et al., J Fermen Bioeng 85:246-249, 1998; U.S. Pat. No. 5,232,842,; Rane et al., Food Biotech 7:11-33, 1993; and Hang, Biotech Lett 12:911-912, 1990.
In general, the cell mass is separated from the fermentation broth and washed with distilled water. The cells are then treated with 0.5 to 2 N NaOH, and the alkaline mixture incubated at 121xc2x0 C. for 15 minutes. The solid material is then pelleted by centrifugation and washed with distilled water and ethanol. The washed material is treated with a 2% acetic acid solution and incubated at 95xc2x0 C. for 12 hours. The resulting slurry is then isolated by centrifugation, yielding an acid-soluble supernatant (containing chitosan) and an acid-insoluble precipitate (containing chitin).
The pH of the supernatant is adjusted to 10 with 2 N NaOH, thereby precipitating out the chitosan. The chitosan is finally washed with distilled water and freeze-dried. The acid-insoluble precipitate is also washed with distilled water and freeze-dried. This acid-insoluble and alkali-insoluble fraction is purified chitin.
Without further elaboration, it is believed that one skilled in the art can, based on the above disclosure and the description below, utilize the present invention to its fullest extent. The following examples are to be construed as merely illustrative of how one skilled in the art can practice the invention and are not limitative of the remainder of the disclosure in any way. Any publications cited in this disclosure are hereby incorporated by reference.